aws-lambda: FilterRule.null() returns empty array

[ujjwol05]

Describe the bug

According to the documentation here, the FilterPattern should be [null]. However, the function FilterRule.null() currently returns an empty array [] instead.

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Version

No response

Expected Behavior

The filter pattern for null should be
{ "eventName": [ "INSERT" ], "dynamodb": { "NewImage": { "test": { "S": [ null ] } } } }

Current Behavior

The filter pattern currently being returned is
{ "eventName": [ "INSERT" ], "dynamodb": { "NewImage": { "test": { "S": [] } } } }

Reproduction Steps

Construct an EventSourceMapping

new lambda.EventSourceMapping(
            this,
            `${stackPrefix}-lambda-event-source-mapping`,
            {
                startingPosition: StartingPosition.TRIM_HORIZON,
                target:XXXX,
                eventSourceArn: XXXX,
                reportBatchItemFailures: true,
                filters: [
                    lambda.FilterCriteria.filter({
                        eventName: lambda.FilterRule.isEqual('INSERT'),
                        dynamodb: {
                            NewImage: {
                                test: { S: lambda.FilterRule.exists() },
                            },
                        },
                    }),
                ],
            }
        );

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.155.0

Framework Version

No response

Node.js Version

v20.11.0

OS

Sonoma

Language

TypeScript

Language Version

No response

Other information

No response

[pahud]

Yes

    new lambda.EventSourceMapping(
      this,
      'demo',
      {
          startingPosition: lambda.StartingPosition.TRIM_HORIZON,
          target: func,
          eventSourceArn: 'mock',
          reportBatchItemFailures: true,
          filters: [
              lambda.FilterCriteria.filter({
                  eventName: lambda.FilterRule.isEqual('INSERT'),
                  dynamodb: {
                      NewImage: {
                          test: { S: lambda.FilterRule.null() },
                      },
                  },
              }),
          ],
      }
  );

would synth to

 demo9A46DC86:
    Type: AWS::Lambda::EventSourceMapping
    Properties:
      EventSourceArn: mock
      FilterCriteria:
        Filters:
          - Pattern: '{"eventName":["INSERT"],"dynamodb":{"NewImage":{"test":{"S":[]}}}}'
      FunctionName:
        Ref: MyFunction3BAA72D1
      FunctionResponseTypes:
        - ReportBatchItemFailures
      StartingPosition: TRIM_HORIZON

which appears to be incorrect per doc.

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